Are you building/buying/flying an Experimental Amateur-Built (E-AB) or Experimental Light Sport (E-LSA) aircraft? Converting an S-LSA to E-LSA? Changing or adding equipment, or otherwise modifying an S-LSA? Need help with Letters of Authorization? Or maybe designing your own aircraft? This forum is the place to discuss All Things Experimental.

I have a set of Intercomp digital scales at my disposal for the next week or so before I return them if anyone has the need to weigh or re-weigh their plane for any reason in the Central Florida / greater Tampa area. Have you added some upgrades to your E-LSA or E-AB and need to redo your W&B? Did you buy a used plane and want to verify the W&B? Whatever the reason I have access to scales. A friend in North Florida who is an A&P-IA loaned me his scales for a fellow EAA builder in my local chapter here in Clearwater who just completed his build. The scales are in my hangar in Zephyrhills (KZPH) if anyone has the need to use them and I'll be returning them in a week or so.

I personally have made several changes and added several options to my plane since I converted to E-LSA and was also in need of a new W&B so they came in handy for me also.

I know most don't need to do this but I wanted to throw this out for anyone who who is curious or wants to weigh their plane in the greater Tampa area for any reason.

If you know the weights and arms of your changes, you can do a recalculated W&B without weighing the airplane again. Since that is an acceptable method to the FAA, I'd always take that option over weighing.

When they get re-weighed, airplanes often mysteriously gain weight, whether from tools &supplies forgotten in the airplane, an "optimistic" original factory weight, or just accumulated dust and grime.

If you calculate the weight, you will be sure you are only adding the weight of your changes. If you get the scales out and they show a bunch of added weight, you are stuck with that number. I would not expose myself to that possibility if I could avoid it.

If you do weigh it, pull everything out that is not essential for flight. A good wash and de-grease would not hurt either.

Thanks for the input Andy, my A&P friend who loaned me the scales also said that airplanes over the years gain weight.

I have added many upgrades to my plane since I purchased it in 2013. Since the plane was already several years old when I bought it and there were equipment changes and upgrades also done by the previous owners in the log books with no update to the W&B, to me putting it on scales gives me the most absolute and accurate answer to her weight. Since the arms of the landing gear and the airplanes MAC didnt change it was easy to input the weight of each wheel into my custom spreadsheet and recalculate my BEW, CG and % MAC very accurately.

I did empty the cockpit of the plane of everything, which was my POH and my headsets. I keep my checklist, fuel strainer, a pen and paper and a flashlight in my center console so those came out as well. Maybe a pound or so of "stuff". And of course drained the fuel. My W&B according to the POH INCLUDES oil, coolant and hydraulic fluids. There has never been any "forgotten tools & supplies" left in my plane. And if you have enough "accumulated dust and grime" to throw off your W&B you need to work on your cleaning skills. Ginger, my plane, gets a sponge bath after every flight.

Again, given the changes over the years, heck I just added a new Odyssey battery that weighs 4 pounds more than the one I took out, the best and most accurate weight comes from the scales and a new calculation. I would rather know EXACTLY what she weighs than ASSUMING the previous weight in the POH or logbook is still accurate and then adding to it. If you didn't know for sure the previous weight was accurate you are essentially adding to an unknown number.

Also it's my opinion that using scales is a lot simpler than trying to measure the arm and weights of all the changes and upgrades over the years. If the part or upgrade is already installed and you dont know the exact weight, you'll simply be guessing. When you added avionics did you weight all the wiring that came with it and what you added? What's the arm of wiring that runs the length of the cockpit and is snaked around and under other wiring and components? What about that new ADS-B, antenna and cable runs? I feel there are simply too many variables to get a truly accurate W&B by measuring the arm and weight of a new component when you dont include ALL the parts for that component other than using scales. My A&P- IA friend who loaned me the scales uses them after he installs or makes upgrades to any aircraft he works on.

I dont see how "exposing" oneself to the scales is a bad thing or why you'd want to avoid it. I now know EXACTLY what my plane weighs and where the CG is. I'll have that warm, fuzzy feeling when I'm calculating my W&B when I throw in a loved one and fill up the tanks.

Again, this is just my opinion and do I feel a little better now knowing my W&B is far more accurate now when I enter weights into my spreadsheet on my iPad. I dont care if the plane added weight over the years. She was light to begin with and so am I so I wasn't going to be concerned with what she weighed.

Once completed a simple log entry into my logbook is all that's needed and it can reference the updated W&B page in my POH.

MrMorden wrote: If you get the scales out and they show a bunch of added weight, you are stuck with that number. I would not expose myself to that possibility if I could avoid it.

On the other hand, from a safety standpoint I'd rather know my plane's actual wt and CG than just what the excel spreadsheet says it is. Especially if you bought the plane used, it may have undergone undocumented mods and repairs that make it heavier than you think. Those can both degrade performance and reduce margins in load factor, stall recovery, and kinetic energy.

Even if all work is documented, things can have changed. FAA says any change of a pound or less is negligible. But how many negligible changes occur over the life of an aircraft? And how many negligibles equal one gligible? Rather than thinking about being "stuck with" the new weigjt, maybe you should consider that you might someday be saved by knowing it.

The opinions posted are those of one CFI, and do not necessarily represent the FAA or its lawyers.Prof H Paul ShuchPhD CFII DPE LSRM-A/GL/WS/PPC iRMTAvSport LLC, KLHVfly@AvSport.orgAvSport.org facebook.com/SportFlyingSportPilotExaminer.US

Gotta agree with Paul. After I changed the panel and avionics, replaced the DC generator/voltage regulator with an alternator/electronic voltage controller, reupholstered and repainted my '63 172, the actual empty weight had increased by fifteen pounds over the calculated empty weight after all the changes. The CG was off a bit as well.

Admittedly there were a lot of changes, but knowing actual empty weight and CG is clearly a safety issue.

Some aircraft's empty weight is calculated without oil, while others are calculated with oil. My preference is to always include oil in the weight and balance, because you are never going to fly without oil. On the other hand some radial engine aircraft have very large oil tanks, and it might be possible to fly a couple gallons low on oil, and that equals 15 pounds difference.

2 Genes? Damn, Stan, I haven't thought about them in decades! I used to give my students supervised solos at South County, when Reid Hillview started getting too busy. That was before we built Frazier Lake Airpark in the early eighties.

The opinions posted are those of one CFI, and do not necessarily represent the FAA or its lawyers.Prof H Paul ShuchPhD CFII DPE LSRM-A/GL/WS/PPC iRMTAvSport LLC, KLHVfly@AvSport.orgAvSport.org facebook.com/SportFlyingSportPilotExaminer.US

The opinions posted are those of one CFI, and do not necessarily represent the FAA or its lawyers.Prof H Paul ShuchPhD CFII DPE LSRM-A/GL/WS/PPC iRMTAvSport LLC, KLHVfly@AvSport.orgAvSport.org facebook.com/SportFlyingSportPilotExaminer.US

Interesting that some aircraft are calculated WITHOUT oil, as stated by 3Dreaming, you're never gonna fly without it. And it's just another line item to add in to your W&B spreadsheet that you might overlook.

I did check my oil and coolant levels before pulling the plane up on the scales. They were both full. I never need to add coolant or oil between my annual condition inspections, it never needs any thankfully.

As Paul stated, knowing the ACTUAL weight and CG of the plane is far safer than calculating in on a spreadsheet. That was my point about the idea of simply knowing the arm and weight and adding it to what could essentially be an unknown number of whatever the last owner may have calculated.

I'm happy to have had the scales to now know exactly where I am with W&B.

MrMorden wrote: If you get the scales out and they show a bunch of added weight, you are stuck with that number. I would not expose myself to that possibility if I could avoid it.

On the other hand, from a safety standpoint I'd rather know my plane's actual wt and CG than just what the excel spreadsheet says it is. Especially if you bought the plane used, it may have undergone undocumented mods and repairs that make it heavier than you think. Those can both degrade performance and reduce margins in load factor, stall recovery, and kinetic energy.

Even if all work is documented, things can have changed. FAA says any change of a pound or less is negligible. But how many negligible changes occur over the life of an aircraft? And how many negligibles equal one gligible? Rather than thinking about being "stuck with" the new weigjt, maybe you should consider that you might someday be saved by knowing it.

I would agree if there were significant questions about the weight of an airplane. In my case I am very sure of the equipment, weights of changes, etc. in my airplane. I’m sure my calculated W&B is within 10lb at the most. I know how my airplane flies and performs at what I have documented at gross weight; there will be no surprises simce I don’t fly over gross.

BTW, my DAR (also the fellow that taught the 16hr ELSA maint. Class I attended) agreed with my reasoning, and said since calculated W&B is acceptable to the FAA, there is no reason not to take advantage of it.

In my case there are very few unknowns, but in the case of an airplane with questionable provenance or modifcation history, or that is not familiar to the pilot, your points make a lot of sense. There is no doubt, of course, that using calibrated scales is the gold standard for accuracy.

Scooper wrote:Gotta agree with Paul. After I changed the panel and avionics, replaced the DC generator/voltage regulator with an alternator/electronic voltage controller, reupholstered and repainted my '63 172, the actual empty weight had increased by fifteen pounds over the calculated empty weight after all the changes. The CG was off a bit as well.

Admittedly there were a lot of changes, but knowing actual empty weight and CG is clearly a safety issue.

Well, you are talking about a 55 year old airplane, that has gone through a lot of changes, and likely several owners. Weighing makes sense there.

Pilots tend to be detail oriented, but we sometimes get the vapors over things that make little difference. In the case of your 172, sure it was 15lb heavier, but is that significant? A 1963172 has a gross of 2450lb, so 15lb is about 0.6% of gross, six-tenths of one percent. Unless that weight is in a 15lb barbell lashed to the rudder, it’s unlikely to be a margin that would significantly impact safety.

Yes, accurate W&B is a safety issue...but to what resolution? One percent of gross? A half a percent, a tenth of a percent, a hundredth? The FAA thinks the resolution provided by an *accurately* calculated W&B is sufficiently safe, and I tend to agree.

In the case of your 172, I’d probably want the scales too, but if I didn’t have the scales available I wouldn’t feel unsafe using a calculated W&B.

Andy, the gross weight of the '63 172D is 2300 lbs, not 2450 lbs, but you're right about 15 pounds not being that big a deal. The problem is that with all the changes I made, I didn't know if it was 15 lbs or 50 lbs, and trying to calculate it would have been more complicated and less accurate than simply weighing it.

Here are the before and after photos, but there's lots of stuff you can't see (autopilot computer and servos, heavier "Real Gaskets" pushrod tubes on the O-300, etc.).